Hand Controlled Manipulation of Single Molecules via a Scanning Probe Microscope with a 3D Virtual Reality Interface

Summary

We demonstrate the precise manipulation of individual organic molecules on a metal surface with the tip of a scanning probe microscope driven in 3D by the experimenter's hand using a motion capture system and fully immersive virtual reality goggles.

Abstract

Considering organic molecules as the functional building blocks of future nanoscale technology, the question of how to arrange and assemble such building blocks in a bottom-up approach is still open. The scanning probe microscope (SPM) could be a tool of choice; however, SPM-based manipulation was until recently limited to two dimensions (2D). Binding the SPM tip to a molecule at a well-defined position opens an opportunity of controlled manipulation in 3D space. Unfortunately, 3D manipulation is largely incompatible with the typical 2D-paradigm of viewing and generating SPM data on a computer. For intuitive and efficient manipulation we therefore couple a low-temperature non-contact atomic force/scanning tunneling microscope (LT NC-AFM/STM) to a motion capture system and fully immersive virtual reality goggles. This setup permits "hand controlled manipulation" (HCM), in which the SPM tip is moved according to the motion of the experimenter's hand, while the tip trajectories as well as the response of the SPM junction are visualized in 3D. HCM paves the way to the development of complex manipulation protocols, potentially leading to a better fundamental understanding of nanoscale interactions acting between molecules on surfaces. Here we describe the setup and the steps needed to achieve successful hand-controlled molecular manipulation within the virtual reality environment.

Introduction

The low-temperature non-contact atomic force/scanning tunneling microscope (LT NC-AFM/STM, in the following simply termed SPM) is the tool of choice for atomically precise manipulation of individual atoms or molecules^1-3. SPM-based manipulation is typically limited to two dimensions and consists of a series of abrupt and often stochastic manipulation events (jumps). This essentially limits the control over the process. Contacting the molecule in question by a single chemical bond at a well-defined atomic position leads to an approach that can overcome these limitations^4-9. Throughout its manipulation th....

Protocol

Caution: PTCDA can be irritating to the skin or eyes and should therefore be handled with care using appropriate gloves. Please consult appropriate safety brochures. Cryogenic liquids can produce effects on the skin similar to a thermal burn or can cause frostbite on prolonged exposure. Always wear safety glasses and appropriate cryogenic gloves when handling cryogenic liquids. The gas formed by cryogenic liquids is very cold and usually heavier than air and can accumulate near the floor displacing air. When there is not enough air or oxygen, asphyxiation and death can occur. Please consult appropriate safety brochures.

1. Sample Preparation

Results

Note: This part shows work published in^7,8.

Applying HCM to the problem of lifting PTCDA/Ag(111) out of a layer, we were able to write a pattern by sequentially removing individual molecules (Figure 9). In total 48 molecules were removed, 40 of which could be redeposited to the clean Ag(111), showing that the molecules stay intact during the manipulation process. This allows using HCM.......

Discussion

Like other SPM-based methods, the molecular manipulation experiments described in this paper also depend to some extent on the properties of the SPM tip. The tip apex structure (which cannot be fully controlled) determines the strength of the tip-molecule bond. Hence the strength of the tip-molecule contact may vary considerably and thus sometimes may be too low. Hence within the protocol we refer to some basic tests of tip quality and tip treatment procedures. However, a more severe tip treatment might be required in so.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
LN2			caution: cryogenic liquid
LHe			caution: cryogenic liquid
PTCDA			caution: irritating substance
Knudsen cell (K-cell)			custom
ErLEED	Specs		used with power supply ErLEED 1,000 A
combient LT NC-AFM/STM	Createc
qPlus sensor	Createc		TFS
preamplifier	Createc		amplifier for tuning fork signal fixed to LN2 shield (stage 1)
Low-Noise Voltage Preamplifier	Standford Research System	SR560	external amplifier for tuning fork signal (stage 2)
Variable Gain Low Noise Current Amplifier	Femto	DLPCA-200	amplifier for tunneling current
Bonita	Vicon	B10, SN: MXBN-0B10-3658	MCS IR camera
Apex Interaction Device	Vicon	SN: AP0062	MCS trackable object (TO)
MX Calibration Wand	Vicon		MCS calibration object
Tracker	Vicon		MCS software
BS series voltage supply	stahl-electronics	BS 1-4	RVS
summing amplifier			custom, gain 1, based on operational amplifier TL072
Oculus Rrift Development Kit 2	Oculus VR		HMD
TipControl			custom-written software
VRinterface			custom-written software